net/mlx5: remove GRE inner IPv6 matching limitation
net/mlx5: remove GRE inner IPv6 matching limitation

Such limitation seems not to exist on:
 - MLNX_OFED_linux-4.5-0.3.0.0 (Beta)
 - MLNX_OFED_LINUX-4.4-2.0.7.0 (GA)
 - upstream kernel 4.19.0-rc7

Signed-off-by: Shahaf Shuler <59427d49da6f2b944fbf4cb5ee70ef3ac25f744f@mellanox.com>
Acked-by: Yongseok Koh <76b37c91816d73ef9cf709e3e83a68f2d162f1e2@mellanox.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk